fix(library): do not emit WorkflowCall outputs and secrets if none set (#1791)

A follow-up after
#1788.

Author: krzema12

github-workflows-kt/src/main/kotlin/io/github/typesafegithub/workflows/domain/triggers/WorkflowCall.kt

@@ -10,8 +10,8 @@ import kotlinx.serialization.Serializable
 @Serializable
 public data class WorkflowCall(
     val inputs: Map<String, Input> = emptyMap(),
-    val outputs: Map<String, Output> = emptyMap(),
-    val secrets: Map<String, Secret> = emptyMap(),
+    val outputs: Map<String, Output>? = null,
+    val secrets: Map<String, Secret>? = null,
     override val _customArguments: Map<String, @Contextual Any> = mapOf(),
 ) : Trigger() {
     @Serializable

github-workflows-kt/src/main/kotlin/io/github/typesafegithub/workflows/yaml/TriggersToYaml.kt

@@ -172,10 +172,10 @@ private fun WorkflowCall.toAdditionalYaml(): Map<String, Any?> =
     when {
         inputs.isEmpty() -> emptyMap()
         else ->
-            mapOf(
+            mapOfNotNullValues(
                 "inputs" to inputs.mapValues { (_, value) -> value.toYaml() },
-                "outputs" to outputs.mapValues { (_, value) -> value.toYaml() },
-                "secrets" to secrets.mapValues { (_, value) -> value.toYaml() },
+                "outputs" to outputs?.mapValues { (_, value) -> value.toYaml() },
+                "secrets" to secrets?.mapValues { (_, value) -> value.toYaml() },
             )
     }
 

github-workflows-kt/src/test/kotlin/io/github/typesafegithub/workflows/yaml/TriggersToYamlTest.kt

@@ -153,6 +153,44 @@ class TriggersToYamlTest :
                     )
             }
 
+            it("renders with just inputs") {
+                // given
+                val triggers =
+                    listOf(
+                        WorkflowCall(
+                            inputs =
+                                mapOf(
+                                    "tags" to
+                                        WorkflowCall.Input(
+                                            description = "Test scenario tags",
+                                            type = WorkflowCall.Type.Boolean,
+                                            required = false,
+                                        ),
+                                ),
+                        ),
+                    )
+
+                // when
+                val yaml = triggers.triggersToYaml()
+
+                // then
+                yaml shouldBe
+                    mapOf(
+                        "workflow_call" to
+                            mapOf(
+                                "inputs" to
+                                    mapOf(
+                                        "tags" to
+                                            mapOf(
+                                                "description" to "Test scenario tags",
+                                                "type" to "boolean",
+                                                "required" to false,
+                                            ),
+                                    ),
+                            ),
+                    )
+            }
+
             it("renders with all parameters") {
                 // given
                 val triggers =